Many of today's highly sensitive electronic components, such as computer and computer-related equipment, that are used in commercial and residential applications contain transient voltage surge suppression (TVSS) devices to protect sensitive and/or expensive electronic circuits and components from damage from over-voltage fault conditions. Such transient voltage surge suppression systems are typically designed for moderate fault conditions that can be expected in normal use. In this respect, such systems are designed to suppress relatively minor fault conditions, but are not designed to protect against major over-voltage conditions such as those that may occur from losing the system neutral or ground termination, or from repetitive current pulses which may occur from lightning strikes. Such major over-voltage conditions can have catastrophic effects on sensitive electronic circuits and components. To prevent such fault conditions from reaching and damaging electronic circuits, components and equipment, it has been known to utilize larger voltage surge suppression devices at a building's incoming electrical service power lines, or within a building's power distribution grid to control power surges in the electrical lines to the building, or in the electrical lines to specific floors of the building. Such voltage surge suppression devices typically include a plurality of metal-oxide varistors (MOVs) connected in parallel between a service power line and a ground or neutral line, or between a neutral line and a ground line.
MOVs are non-linear electronic devices made of ceramic-like materials comprising zinc-oxide grains and a complex amorphous inner granular material. Over a wide range of current, the voltage remains within a narrow band commonly called the varistor voltage. A log-log plot of the instantaneous voltage in volts versus the instantaneous current in amps yields a nearly horizontal line. It is this unique current-voltage characteristic that makes MOVs ideal devices for protection of sensitive electronic circuits against electrical surges, over-voltages, faults or shorts.
When exposed to voltages exceeding their voltage value, MOVs become conductive devices that absorb the energy related to the conductive state and limit dump current to a neutral line or ground plane, thus dissipating some of the excessive power. In addition, when exposed to voltages exceeding their voltage value, MOVs generate heat based upon the over-voltage, thus dissipating some of the over-voltage condition as heat. However, if an over-voltage condition is not discontinued, the MOVs will continue to overheat and eventually can catastrophically fail, i.e., rupture or explode. Such catastrophic failure may destroy the sensitive electronic equipment and components in the vicinity of the MOVs. The destruction of electrical equipment or components in the electrical distribution system can disrupt power to buildings or floors for prolonged periods of time until such components are replaced or repaired. Moreover, the failure of the MOVs in a surge suppression system may allow the fault condition to reach the sensitive electronic equipment the system was designed to protect.
The present invention provides a circuit protection device and a transient voltage surge suppression system incorporating such device to protect an electrical system from catastrophic failure due to excessive over-voltage conditions or repetitive fault conditions.